1. Field of the Invention
The invention is directed to an improved fuel injection apparatus for an internal combustion engine of the type including a fuel supply pump that delivers fuel to at least one high pressure pump which in turn delivers high pressure fuel to a reservoir.
2. Description of the Prior Art
A fuel injection apparatus known from DE 198 53 103 A1 has a fuel supply pump that delivers fuel to at least one high-pressure pump, which in turn delivers highly pressurized fuel to a reservoir. In addition, a fuel metering device is provided between the fuel supply pump and the high-pressure pump. The fuel metering device serves to control the quantity of fuel that the high-pressure pump delivers into the reservoir in accordance with operating parameters of the internal combustion engine. The fuel metering device includes an actuator in the form of an electromagnet and a check valve that is actuated by it, which has a slider-shaped valve element that is guided in a cylindrical bore of a valve housing and can be slid by an armature of the electromagnet in opposition to a return spring. The outer circumferential surface of the valve element, in cooperation with an outlet opening in the valve housing, controls a flow cross section from the fuel supply pump to the high-pressure pump in a stroke-dependent manner. When the valve element is in a closed position, its outer circumferential surface overlaps the outlet opening so that the flow cross section is completely closed. But since the valve element must be able to slide in the cylindrical bore of the valve housing, there must be a slight amount of play between its outer circumference and the cylindrical bore, through which a leakage quantity of fuel can flow and travel via the outlet opening to the high-pressure pump, even when, due to the operating parameter of the engine, for example when overrunning, the high-pressure pump is not supposed to deliver any fuel, during a so-called zero delivery. It is therefore necessary for steps to be taken in order to drain away this leakage quantity of fuel so that it cannot travel to the high-pressure pump and so that the zero delivery is achieved. To this end, a throttled connection to a discharge region can be provided; but in this case, fuel downstream of the fuel metering device constantly drains into the discharge region and in addition, there is an increased pressure level between the fuel metering device and the high-pressure pump. In order to prevent the high-pressure pump from taking in fuel, the opening pressure of at least one intake valve of the high-pressure pump must be set to a correspondingly high level; this, however, has a negative impact on the volumetric efficiency of the high-pressure pump. On the whole, this consequently requires a more complex design and more expensive manufacture of the fuel injection apparatus.